And I'm Steve Inskeep. BP faces trial next week in a civil lawsuit to fix blame for the worst environmental disaster in U.S. history. It's the 2010 explosion of the Deepwater Horizon in the Gulf of Mexico.

MONTAGNE: Eleven rig workers were killed and nearly five million barrels of oil spilled. Some of the oil drifted onto beaches and wetlands from Florida to Texas.

INSKEEP: And now tens of billions of dollars in civil penalties are at stake. NPR's Debbie Elliott reports.

DEBBIE ELLIOTT, BYLINE: The three main issues before a New Orleans federal judge are whether BP was grossly negligent, how much oil polluted the Gulf, and what kind of environmental harm it caused. Many observers anticipated a settlement, but as trial draws near, all sides appear to be digging in for a court battle. Alabama Attorney General Luther Strange is coordinating counsel for the five Gulf states.

ATTORNEY GENERAL: We think BP was grossly negligent and we are prepared to prove that starting on the 25th.

ELLIOTT: Yesterday, BP general counsel Rupert Bondy acknowledged the company was looking to make a deal, but said in his statement that, quote, "faced with demands that are excessive and not based on reality, we are going to trial." That's something BP CEO Bob Dudley prepped investors for in a conference call.

BOB DUDLEY: Throughout we have been preparing for the trial scheduled for later this month and we will be ready to thoroughly and factually present our case in court.

ELLIOTT: BP says the disaster was a tragic accident resulting from multiple causes and involving multiple companies. Some, including rig owner Transocean, have settled both criminal and civil charges. BP has admitted its role in the accident and reached a record $4.5 billion dollar criminal deal with the Justice Department.

Sources close to the ongoing civil talks say states are the holdup, in part because of the enormous amount of money involved. It's complicated. First, there are clean water act penalties - the bulk of which will go back to the Gulf states.

The range is about five billion up to $20 billion, depending on whether the judge finds that BP was grossly negligent. That's why you'll hear lawyers like Alabama Deputy Attorney General Corey Maze argue that BP could have prevented the deadly well blowout.

DEPUTY ATTORNEY GENERAL COREY MAZE: What we're going to prove is a corporate culture of just callousness. Every decision you're going to see that BP made or didn't make was because it saved them time and money.

ELLIOTT: BP says it will vigorously defend the allegations and will also dispute the government on how much oil spilled. Clean water act penalties are calculated per barrel.

DAVID UHLMAN: If this case goes to trial, it is a high stakes gamble for everyone involved.

ELLIOTT: University of Michigan law professor David Uhlman is a former chief of the Justice Department's environmental crime section. He says the bigger sticking point is what BP should pay for natural resource damages - for instance, fisheries harmed or wetlands destroyed.

UHLMAN: And that's a real wild card in the Gulf because no one really knows how much damage was done by the Gulf oil spill.

ELLIOTT: Environmentalists don't want to see the Gulf shortchanged.

UNIDENTIFIED MAN: All right, let's go.

ELLIOTT: Last week in Washington, a coalition of groups delivered boxes of petitions to Attorney General Eric Holder. Sara Gonzales-Rothi is with the National Wildlife Federation.

SARA GONZALES-ROTHI: They say make BP pay, hold BP fully accountable.

ELLIOTT: It's been nearly three years since the oil spill, but the disaster is far from over. Off the Alabama coast, for example, submerged tar mats continue to wash up during rough surf. And Louisiana still has over 200 miles of oiled shoreline.

Contending with that, and an uncertain future, is what's holding Louisiana back from making a deal, says Garret Graves, the top coastal advisor to Governor Bobby Jindal.

GARRET GRAVES: If we pivot to a settlement type scenario, it would be a settlement that we can stand before the citizens of the Gulf of Mexico and explain to them, defend to them, and ensure that the long term interests of the Gulf are fully addressed. Not just this generation but for generations to come.

ELLIOTT: Generations that could still be contending with BP's oil long after the complicated litigation has been resolved. Debbie Elliott, NPR News, Orange Beach, Alabama. Transcript provided by NPR, Copyright NPR.